1. Field of the Invention
The present invention relates to a method for synthesizing an analysis model automatically according to a shape or the like of an object to be analyzed, and a flow analysis system which evaluates and designs a flowpassage of a mold, a resin characteristic and a molding condition from a flow state of resin.
2. Description of the Prior Art
In numerical analysis for the design of products, generally, a shape of an object to be designed is mathematically modelled. According to the latest CAE system, modelling (mesh automatic division when a finite element method is used) of a shape-defined product is automatically carried out, for example, as shown in "Mold Technique - Data Book For Mold For Plastic Injection Molding" (Vol. 2, No. 11, Oct. 20, 1987, issued by Nikkan Kogyo Shimbunsha), Chapter 2 (Runner and Gate), pages 16 to 19.
Further, in a conventional system, in designing a mold for housings such as used for electric appliances for home-use, a fluidity of a thermoplastic resin as a material is evaluated. In designing, the matter of importance is an external shape of a product, which is related to the design thereof.
The above-described prior art has paid no attention to the following points and could not be applied to the design of a molding die for semiconductors.
(1) Conventional model generation methods are peculiar to analysis program using analysis procedures, such as a finite element method and a difference calculus, and therefore, no consideration has been given to the situation in which plurality of analysis programs are combined to form an analysis model. An analysis model is not formed by combining a plurality of analysis programs in a manner such that one part of an object to be analyzed is worked out by a difference calculus while the other is worked out by a finite element method, or one part is worked out by an analysis program (1) according to the difference calculus while the other worked out by an analysis program (2) according to the difference method, but preparation of a model is exclusively carried out by an analyst. Therefore, the prepared analysis model is characterized by individual difference results depending on the experience of the analyst in preparing models or on the difference in knowledge about the analysis program. It generally takes much time to prepare a model.
(2) Semiconductor plastic packages are made of thermoset resin instead of thermoplastic resin used for housings, such as for electric appliances for home-use. The thermoset resin is a material which absorbs heat from a mold during molding to induce hardening reaction whereby viscosity is changed in a complicated way. It is therefore necessary to make an accurate estimate of change in viscosity of resin during molding.
A cavity portion of a mold for a semiconductor includes therein internal elements such as a lead frame, chips, Au wires, etc. which constitute a semiconductor, which may possibly be greatly deformed due to the flow of resin during molding. The quality of semiconductor products is directly affected by the deformation of these internal elements. Accordingly, it is necessary to evaluate not only the filling state of the resin, but also the influence thereof on the internal elements. However, when the internal elements are placed in a flowpassage of the mold which is in the form of a flattened and narrow configuration, not only the internal elements are deformed, due to the flow of the resin, but the state of flow of the resin is greatly changed. It is difficult to develop a program for analyzing (simulation) the change which occurs. The reason is that in order to model the state of flow of the resin resulting from the internal elements to reflect on the program, improvements have to be made while adjusting to a number of experimental data, for which long periods and many steps are required, as mentioned in the aforementioned paragraph (1). Actually, it is impossible to repeat such a trial-and-error program development for every product.
(3) As mentioned in the above-described paragraph (2), in order to analyze the deformation of the internal elements in the mold and the like, it is necessary to perform a stress analysis and the like from not only the flow state of the resin, but also from the viscosity, flow velocity, pressure and the like obtained from the flow state. However, an analysis program is prepared so that data required by the analysis to be carried out by said program is input in a specific form, and the output data is output in the form suitable for expressing the result. Therefore, in the case where a plurality of analysis programs are used to perform analysis, it is necessary to convert input and output data. To this end, considerable knowledge of the function of programs and input and output is required as mentioned in the above-described paragraph (1), and it is difficult to perform such analysis.